QwtBezier Class Reference

An implementation of the de Casteljau’s Algorithm for interpolating Bézier curves. More...

#include <qwt_bezier.h>

List of all members.

Public Member Functions
void	appendToPolygon (const QPointF &p1, const QPointF &cp1, const QPointF &cp2, const QPointF &p2, QPolygonF &polygon) const
	Interpolate a Bézier curve by a polygon.
	QwtBezier (double tolerance=0.5)
	Constructor.
void	setTolerance (double tolerance)
double	tolerance () const
QPolygonF	toPolygon (const QPointF &p1, const QPointF &cp1, const QPointF &cp2, const QPointF &p2) const
	Interpolate a Bézier curve by a polygon.
	~QwtBezier ()
	Destructor.
Static Public Member Functions
static QPointF	pointAt (const QPointF &p1, const QPointF &cp1, const QPointF &cp2, const QPointF &p2, double t)
Private Attributes
double	m_flatness
double	m_tolerance

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Detailed Description

An implementation of the de Casteljau’s Algorithm for interpolating Bézier curves.

The flatness criterion for terminating the subdivison is based on "Piecewise Linear Approximation of Bézier Curves" by Roger Willcocks ( http://www.rops.org )

This article explains the maths behind in a very nice way: https://jeremykun.com/2013/05/11/bezier-curves-and-picasso

Definition at line 27 of file qwt_bezier.h.

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Constructor & Destructor Documentation

QwtBezier::QwtBezier

(

double

tolerance = 0.5

)

Constructor.

Parameters:

tolerance

Termination criterion for the subdivision

See also:

setTolerance()

Definition at line 113 of file qwt_bezier.cpp.

QwtBezier::~QwtBezier

(

)

Destructor.

Definition at line 120 of file qwt_bezier.cpp.

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Member Function Documentation

void QwtBezier::appendToPolygon	(	const QPointF &	p1,
		const QPointF &	cp1,
		const QPointF &	cp2,
		const QPointF &	p2,
		QPolygonF &	polygon
	)		const

Interpolate a Bézier curve by a polygon.

appendToPolygon() is tailored for cummulating points from a sequence of bezier curves like being created by a spline interpolation.

Parameters:

p1	Start point
cp1	First control point
cp2	Second control point
p2	End point
polygon	Polygon, where the interpolating points are added

Note:

If the last point of the incoming polygon matches p1 it won't be inserted a second time.

Definition at line 183 of file qwt_bezier.cpp.

QPointF QwtBezier::pointAt	(	const QPointF &	p1,
		const QPointF &	cp1,
		const QPointF &	cp2,
		const QPointF &	p2,
		double	t
	)		[inline, static]

Find a point on a Bézier Curve

Parameters:

p1	Start point
cp1	First control point
cp2	Second control point
p2	End point
t	Parameter value, something between [0,1]

Returns:

Point on the curve

Definition at line 70 of file qwt_bezier.h.

void QwtBezier::setTolerance

(

double

tolerance

)

Set the tolerance

The tolerance is a measurement for the flatness of a curve. A curve with a flatness below the tolerance is considered as being flat terminating the subdivision algorith.

When interpolating a Betier curve to render it as a sequence of lines to some sort of raster ( f.e to screen ) a value of 0.5 of the pixel size is a good value for the tolerance.

Parameters:

tolerance

Termination criterion for the subdivision

See also:

tolerance()

Definition at line 138 of file qwt_bezier.cpp.

double QwtBezier::tolerance

(

)

const [inline]

Returns:

Tolerance, that is used as criterion for the subdivisn

See also:

setTolerance()

Definition at line 54 of file qwt_bezier.h.

QPolygonF QwtBezier::toPolygon	(	const QPointF &	p1,
		const QPointF &	cp1,
		const QPointF &	cp2,
		const QPointF &	p2
	)		const

Interpolate a Bézier curve by a polygon.

Parameters:

p1	Start point
cp1	First control point
cp2	Second control point
p2	End point

Returns:

Interpolating polygon

Definition at line 154 of file qwt_bezier.cpp.

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Member Data Documentation

double QwtBezier::m_flatness [private]

Definition at line 47 of file qwt_bezier.h.

double QwtBezier::m_tolerance [private]

Definition at line 46 of file qwt_bezier.h.

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The documentation for this class was generated from the following files:

• qwt_bezier.h
• qwt_bezier.cpp